ASTM D6296 Standard Test Method for Total Olefins in Spark-ignition Engine Fuels
ASTM D6296 Standard Test Method for Total Olefins in Spark-ignition Engine Fuels by Multi-dimensional Gas Chromatography
9. Preparation and Setup of Apparatus
9.1 Assemble the analyzer system (gas chromatograph with independent temperature controlled components) as shown in Fig. 1 or with an equivalent flow system. If using a commercial system, install, place the system in service, and optimize the system in accordance with the manufacturer's instructions.
NOTE 10 - Commercial systems will have all parameters predetermined and accessible through the software. Other constructed systems will require experimentation and optimization of parameters to achieve the required separation and precision.
9.2 Impurities in the helium carrier gas, hydrogen, or air will have a detrimental effect on the performance of the columns and traps. Therefore, install efficient purifiers in the gas lines as close to the system as possible and use good quality gases. The helium and hydrogen gas connection lines shall be made of metal. Check that all gas connections, both exterior and interior to the system, are leak tight.
9.3 Verify that the ether/alcohol trap conditions satisfactorily retain ethers. Analyze Set Up Mixture 1 or 2, depending on whether samples contain MTBE or ETBE, using a method to set the switching valves so that only the non-polar column and ether/alcohol trap are in the flow path. Determine the elution time of the MTBE (or ETBE). The ether/alcohol trap conditions are satisfactory if the ether peak begins to elute after 5.5 min and the peak shows a steep frontal portion. If the ether peak begins to elute earlier or the frontal is not steep, decrease the temperature of the ether/alcohol trap and reoptimize the system.
NOTE 11 - If the oxygenate composition is unknown, the sample will require analysis by Test Method D4815, D5599, or other test methods. If it is found that ETBE is present, only C4 through C9 olefins can be determined.
9.4 Optimize the olefin trap temperature by analyzing Calibration Standard 1 or 2 as described in 10.3, depending on whether samples contain MTBE or ETBE. A typical chromatogram is shown in Fig. 2. Verify that undecane is completely eluted before 10 min while penetene is quantitatively (see Note 12) retained. If the undecane has a longer retention time, the olefin trap temperature must be increased. If pentene is not being quantitatively retained, the olefin trap temperature must be decreased. Adjust the olefin trap temperature as necessary, and reanalyze the calibration standard until the above conditions are met.
NOTE 12 - As compared to the precision statement (see Table 5).
9.5 Analyze the quality control sample, see 8.8. Verify that results are consistent with those previously obtained and that C4 and C5 olefins are quantitatively (see Note 12) retained by the olefin trap. If C4 and C5 olefins are not quantitatively retained, reoptimize the olefin trap temperature (see 9.4).
9.5.1 Reoptimize the system (see 9.1) whenever the QC sample results do not conform to those expected.
